1. Field of the Invention
The present invention relates to an image pickup device such as a video camera and a monitoring camera and to a control method for the image pickup device.
2. Description of the Related Art
Conventionally, image pickup devices such as a video camera and a monitoring camera have been in widespread use which is capable of changing the shooting direction freely by controlling the camera unit by a pan mechanism and a tilt mechanism which are driven by motors, respectively.
For example, while shooting an object of shooting (hereinafter referred to as “an object”) with a monitoring camera, if a target object is a human or an animal, generally the operator of the monitoring camera traces the object by an operation of moving the direction of a camera lens while watching the screen of a monitor, but if movement of the direction of the camera lens is too slow or too fast, the object may be lost. Therefore, an automatic tracing function to automatically trace the object is desired to be provided.
Also, while shooting an object by a video camera for example, if movement of a target object changes largely or quickly, it is difficult to manually trace the object. Therefore, an automatic tracing function to automatically trace an object is desired to be provided (for example, refer to Japanese Laid-open Patent Publication (Kokai) No. H07-23271).
Further, for example, while operating a video camera, sometimes it may be troublesome to manually change its zoom magnification. For example, when shooting a scene of a relay race or the like in an athletic festival with a video camera, manually changing the zoom magnification while pressing down a recording button of the video camera causes an object inside a shot image to be unfavorably too big or too small.
Accordingly, an automatic zoom function to automatically adjust the zoom magnification with the traced object as a center is desired, but in the current situation, such a function is not proposed.
In recent years, as a drive source for driving a camera lens or the like, an ultrasonic motor is adopted.
FIG. 22 is a schematic view showing an overall structure of a typical ultrasonic motor.
In FIG. 22, reference numeral 2201 denotes an oscillator comprising piezoelectric elements layered one after the other. Then, by supplying an A-phase signal 2208 and a B-phase signal 2209 as signals having a certain frequency to the oscillator 2201, its resonance generates a mechanical traveling wave in an arrow 2205 direction or in an arrow 2206 direction.
The oscillation of the oscillator 2201 is amplified mechanically by a stator 2202 attached to this oscillator 2201. Then, a rotor 2203 in pressure-contact with the stator 2202 via a rib 2207 turns in the arrow 2205 direction or the arrow 2206 direction in the drawing. This turning of the rotor 2203 is transmitted to a shaft 2204 to generate its turning movement.
A characteristic of the ultrasonic motor having such a structure is a short accelerating/decelerating time during driving.
FIG. 23 is a graph showing a turning speed of a typical brushless motor, in which the abscissa axis and the ordinate axis represent time and the turning speed of the motor, respectively.
In the case of the brushless motor, as shown in FIG. 23, it takes a time of 400 ms to reach a turning speed of 300°/second.
FIG. 24 is a graph showing a turning speed of a typical ultrasonic motor (USM), in which the abscissa axis and the ordinate axis represent time and the turning speed of the motor, respectively.
In the case of the ultrasonic motor, as shown in FIG. 24, the time required for reaching the turning speed of 300°/second is only 20 ms, and thus it can operate with a shorter acceleration/deceleration speed as compared to the brushless motor.
The automatic tracing function as described above is adopted in monitoring cameras or the like which are already commercialized, but the drive motor for a pan mechanism and a tilt mechanism for changing the direction of a camera lens is a brushless DC motor or a stepping motor. Such a motor can accelerate/decelerate only at a low speed, and therefore in the current situation, it cannot respond to quick movement of an object.
Also, since conventional motors are not able to stop quickly, a shooting operation is performed while performing a turning operation as disclosed in Japanese Laid-open Patent Publication (Kokai) No. H07-23271, thereby resulting in a flow of a shot image or the like to deteriorate its image quality.
Further, a camera having an automatic zoom function to control a zoom lens by an ultrasonic motor is commercialized, but a video camera having the automatic zoom function in conjunction with the automatic tracing function as described above does not exist. Accordingly, there has been a complication in operation such that the zoom function has to be controlled by a manual operation while shooting with a video camera.
Also, when the ultrasonic motor is used as it is to drive the pan mechanism, the tilt mechanism or the zoom mechanism, the ultrasonic motor operates at high speed while shooting, which provides a problem that the shot image flows and the image quality deteriorates, thereby disabling the object to be specified when processing an image to specify the object during tracing.